The present invention relates to an impeller housing for a suction device. More particularly, it relates to an improved impeller housing which has reduced noise and improved airflow.
In a "dirty air" vacuum cleaner, the debris passes directly through the vacuum impeller chamber prior to being captured by the cleaner bag. In contrast, a "clean air" vacuum cleaner has the motor drawing the air and debris through the bag so that the bag captures the debris. The air only subsequently passes through the impeller chamber. The dirt path in a dirty air vacuum cleaner is very short compared to most clean air systems, which has advantages for cleaning performance. One disadvantage of dirty air motors is that they are typically louder than clean air motors. They also have a very loud tone noise. While not the largest contributor to the overall noise levels, the tone noise can be very annoying to consumers.
Tone noise typically occurs at a frequency that is seven times the rotation rate of the motor, which corresponds to the seven blades of the typical working fan. The motor cooling fan typically has twelve blades, is small, and may not, therefore, be a source of additional tone noise as was the case in the particular motor studied. The working fan blades cause the tone noise when they pass a geometric discontinuity in the volute shape. For example, FIG. 1 shows a cross section of the volute with the fan blades of an existing design. FIG. 1 also shows a geometric discontinuity at the motor outlet that causes tone noise. There is usually no geometric discontinuity at the motor inlet. Such discontinuities cause noise by interacting with the airflow leaving the ends of the blades. The airflow leaving the end of the blades is chopped by the discontinuities at the rate that the blades pass these discontinuities.
For noise control, there are two primary solutions. One is to isolate the noise source so that it is not heard; the other is to reduce the noise source. Isolating the noise source is an expensive choice. However, it does not require a good understanding of the noise source mechanism to be effective. The preferred solution is to reduce the source of noise.
Reducing the interaction of the airflow from the blade ends with the volute exhaust opening reduces the source of tone noise. Several ways to accomplish this are a) increasing the distance between the outer wall of the volute and the fan blade tips, b) reducing the fan rotation rate to reduce air velocity off the fan blade tips, and c) eliminating the geometric discontinuities, by moving the exhaust opening below the volute or on a different plane from the volute so that the fan blades are enclosed in a constant cross-section volute.
The first option, increasing the distance between the outer wall of the volute and the fan blade tips, has been used in several designs, but with limited success.
The second option, reducing the air velocity, reduces the noise level by approximately the velocity cubed. Reducing the air velocity would be accomplished by reducing the rpm of the motor or reducing the size of the working fan while maintaining the motor speed. Care must be taken when just reducing the size of the working fan because the motor would speed up due to the reduced load, which can result in the same velocities. If this solution were implemented, then the broadband noise would also be reduced because the broadband noise due to air turbulence decreases as the velocity decreases. However, reducing the fan rotation rate to reduce air velocity off the fan blade tips is not considered feasible because the current trend of U.S. vacuum cleaners has been to obtain as large an electrical amperage rating as possible.
Therefore, the third option, eliminating geometric discontinuities by moving the exhaust opening to below the volute or to a different plane from the volute, is the most feasible solution.
This option reduces the tone noise by removing the source of the noise. The goal is for the space around the fan tips to be in the shape of a uniform ring. Space is then provided for the air to exit behind the fan.
Accordingly, it has been considered desirable to develop a new and improved impeller housing which would overcome the foregoing difficulties and others and meet the above stated needs while providing better and more advantageous overall results.